Fix for byte-compile warnings

I got following error when byte-complied.

```
Compiling file /home/syohei/tmp/gomi/elisp/toggle.el at Tue Aug 19 15:08:51 2014
Entering directory `/home/syohei/tmp/gomi/elisp/'
toggle.el:64:1:Warning: cl package required at runtime

In toggle-style:
toggle.el:129:37:Warning: `interactive-p' is an obsolete function (as of
    23.2); use `called-interactively-p' instead.
toggle.el:129:21:Warning: assignment to free variable `toggle-mappings'
```